Illuminating apparatus is usually used to provide the illuminating effect in the dark ambience. However, the luminance of illuminating apparatus is usually fixed with a constant illuminating intensity. In other words, when the illuminating apparatus is turned on, the power consumption usually remains the same. Although some of the illuminating apparatuses allow to change the luminance by adjusting the duty cycle to adapt the brightness in the ambience, it is not adjusted according to the visual effect of human eyes. As usually known, the luminance efficacy of human eyes at the photopic state and the scotopic state have different response curves with respect to the wavelength. When the ambience is at dim state, the response of eye with respect to wavelength is based on the curve of mesopic state. Therefore, the proper luminance needs to be adjusted according to the response curve of human eyes at the mesopic state.
How to automatically adjust the luminance of lighting source is an issue under consideration when designing the light source.